Semiconductor devices of BGA (ball grid array) and LGA (land grid array) package types have conventionally been known. In the semiconductor devices of these types, external connecting electrodes of a chip carrier on which a semiconductor device is mounted are arranged like a grid on the back face thereof. These semiconductor devices have the external connecting electrodes provided on the back of a package so that the size can greatly be reduced as compared with a conventional semiconductor device of a QFP (Quadflat package) type. The pitch of the external connecting electrodes is 1.5 or 1.27 mm, while the semiconductor device of a QFP type has a pitch of 0.3 or 0.5 mm. Consequently, mounting can be performed easily. For this reason, the semiconductor devices of BGA and LGA package types have attracted favorable notice.
FIG. 8 shows a semiconductor device of a BGA package type according to the prior art. In FIG. 8, 1 designates a chip carrier, 2 designates a solder ball, 3 designates a semiconductor device, and 4 designates an external connecting electrode. The chip carrier 1 has a structure in which a connecting wiring 61 is provided on a surface 60a of an electrical insulating board 60 and the external connecting electrode 4 is provided on a back face 60b of the electrical insulating board 60. The connecting wiring 61 is conducted to an electrode pad 31 of the semiconductor device 3. The connecting wiring 61 of the surface 60a and an external drawing electrode 62 of the back face 60b are electrically conducted through a wiring 64 and the like provided in a through hole 63. The through hole 63 conducts both faces of the electrical insulating board 60.
As the external connecting electrodes of a BGA package type, the solder balls 2 are arranged like a grid on the back face of the chip carrier 1. The connection to a circuit wiring board (not shown) can be obtained by the solder balls 2. The semiconductor device of a LGA package type has a structure in which the connection to the circuit wiring board can be obtained by a solder having no ball or a socket.
As compared with the semiconductor device of a LGA package type, the semiconductor device of a BGA package type uses the solder balls for mounting so that the mounting space between the chip carrier and the circuit wiring board is large. Consequently, the semiconductor device of a BGA package type has the higher mounting reliability upon solder mounting than that of a LGA package type. For this reason, the semiconductor device of a BGA package type which has the external connecting electrodes arranged like a grid has been commonly used. However, in a semiconductor device which should be developed, for example, a CPU of a computer, the combination of the LGA and the socket is often used.
However, in the case where the conventional chip carrier of a BGA or LGA package type is mounted on the circuit wiring board by a solder, the following troubles are caused. More specifically, the chip carrier is directly connected to the circuit wiring board by the solder. For this reason, when an environmental reliability test such as a thermal shock test, which changes a temperature from -40.degree. C. to 100.degree. C., is given as defined by JIS C0025, the external connecting electrode portions crack, the external connecting electrodes peel off and the connection becomes poor due to a difference between the coefficients of thermal expansion of the chip carrier and the circuit wiring board. Thus, BGA and LGA package types have poor reliability in the thermal shock test.